%I A145846
%S A145846 1,2,8,47,357,3270,34515,406460,5215829,71677058,1041363040,15841778155,
%T A145846 250494079945,4093630537014
%N A145846 Number of permutations of length 2n which are invariant under the reverse-complement 
               map and have no decreasing subsequences of length 6.
%F A145846 a(n) = sum(j, 0, n, C(n,j)^2 * A000108(n-j) * A005802(j)),
%F A145846 where C(n,j) = n!/(j!(n-j)!)
%t A145846 Table[Sum[ Binomial[n, j]^2*((1/(n - j + 1))* Binomial[2*(n - j), n - 
               j]/((j + 1)^2*(j + 2)))* Sum[Binomial[2*i, i]*Binomial[j + 1, i + 
               1]* Binomial[j + 2, i + 1], {i, 0, j}], {j, 0, n}], {n, 0, 20}]
%Y A145846 Sequence in context: A096656 A102009 A135904 this_sequence A009566 A003275 
               A078558
%Y A145846 Adjacent sequences: A145843 A145844 A145845 this_sequence A145847 A145848 
               A145849
%K A145846 nonn
%O A145846 0,2
%A A145846 Eric Egge (eegge(AT)carleton.edu), Oct 21 2008